1. Field of the Invention
The present invention generally relates to a magnetic disc apparatus, and more particularly to a flexible printed circuit sheet employed for transmission of electrical signals between a rocking type actuator of the magnetic disc apparatus and external electrical circuits.
2. Description of the Prior Art
Conventionally, in a magnetic disc apparatus as referred to above, since flexibility is required for effecting electrical wirings to a magnetic head 3' (FIG. 4.) subjected to rocking driving together with a rocking type actuator 2-1' and a voice coil motor (referred to as a VCM hereinafter) 2-4', etc., a flexible printed circuit sheet (referred to as FPC hereinafter) 1-1' has been employed as shown, for example, in a known magnetic disc apparatus of FIG. 4. In the known arrangement of FIG. 4, a flexible bending portion 1-2', subjected to a bending motion as the rocking type actuator 2-1' is driven, is branched from an apparatus fixing portion 1-3' folded back at right angles, and is fixed, in the bent state, to an FPC fixing portion 2-3b' provided on the outer wall of a rotor 2-3a', and thus repeatedly bent and extended following driving of the rocking type actuator 2-1' as shown in FIG. 5, in which acting directions of reaction forces are represented by numeral 5', and driving forces by numeral 6'. In the above case, the FPC fixing portion 2-3b' has a shape making a certain angle so that it may not contact other members during driving of the flexible bending portion 1-2', while the flexible bending portion 1-2' is also limited to a length so that it will not contact other members.
In the conventional construction as described above, however, a reaction force in one direction due to a restoring force of the flexible bending portion 1-2' is applied at all times to the FPC fixing portion 2-3b' and the rotor 2-3a', i.e. to the rocking type actuator 2-1'. Such a reaction force not only results in a loss of torque in the VCM 2-4', but adverse affects such as an offset or the like may result during tracing of the data track. Therefore, the conventional practices for eliminating such disadvantages have been such that the length of the flexible bending portion 1-2' is increased as far as possible, and its width is reduced in order to minimize the reaction force, while the bending radius thereof is set to be as large as possible, and moreover, the flexible bending portion 1-2' is attached so that the reaction force is directed in a direction perpendicular to the driving direction of the rocking type actuator 2-1'. However, the practices as described above do not necessarily provide solutions to the problem, due to limitations in the reduction of size and the configuration of the apparatus, and accordingly it becomes necessary to provide a method generally applicable to any type of apparatus. Meanwhile, in order to realize a thin type of drive, it becomes necessary to reduce the width of the flexible bending portion 1-2', thus requiring a narrowing of the pattern intervals, but at the present stage, it is difficult to narrow the intervals more than a certain level in order to satisfy the strength, performance and manufacturing limits, etc. Furthermore, there is another defect in that, for reducing intervals between patterns, noises between the head line and the VCM line are undesirably carried by the signals from the magnetic head.